The present invention is concerned with a process, and the devices for implementing it, which assures the suppression of harmful factors and permits the elimination of at least the majority of the ecologically objectionable pollutant elements--noxious or undesirable due to their toxicity, their odor, and their opaqueness--contained in the gas or liquid wastes discarded by installations manufacturing mineral fibers, and which also assures reduction of the noise produced by these same installations.
The invention is concerned with installations for the manufacturing of fiber blanket, mat padding, or boards of mineral fibers and especially glass, agglomerated by thermosetting or thermoplastic binders, which coat the fibers and/or bring about close binding between fibers in the finished product.
The binders commonly used in this type of manufacturing have a base consisting of pure or modified phenoplast or aminoplast resins, since these present advantageous characteristics for the manufacturing of agglomerated fibrous products. They are thermohardenable, soluble or emulsifiable in water, they adhere well to the fibers, and are relatively low in cost.
Generally, these binding agents are used dissolved or dispersed in water to which certain ingredients are added, in order to form the binder which is sprayed on the fibers.
Under the effect of the heat to which they are subjected during the fiber products manufacturing processes, these binders release toxic volatile elements having a perceptible pungent odor even at very weak concentrations, such as phenol, formaldehyde, urea, ammonia, and decomposition products of organic materials.
Other binders are used for certain applications due to their very low cost. Certain extracts of natural products are hardened by drying and cross linking, such as occurs with linseed oil upon oxidation. Others are thermoplastic, as for example bitumen. During the fiber binding process, they are all, at least to some extent, increased in temperature and to a temperature sufficient to cause the release of volatile elements, noxious or otherwise undesirable, amont other reasons, due to their odor.
In the text below, the word "binder" will be used to designate any one or all of the binding products mentioned above, whether they are used in liquid form, dissolved or suspended in water or in other liquid, or in an emulsion.
The invention relates to that part of the installation for manufacturing agglomerated fibrous materials called the fiber collecting or forming section, which is situated immediately after the fiber production apparatus, and in which the following operations are carried out primarily:
the conveying of the fibers from the fiber production apparatus to the mat or blanket forming equipment;
the application of the binder to the fibers, the binder generally incorporating pollutant elements;
the formation of the blanket on the fiber collecting device, for which purpose the collecting device generally consists of a perforated belt;
the cooling of the fibers and of the gases used for attenuating or guiding the fibers, such cooling generally being accomplished by air induced by the gases;
the separation of the fibers from the gases and induced air by suction these fluids through the blanket being formed; and
the evacuation outside of the installation of all the elements not retained by the fiber blanket or the mat being made.
It is in the fiber collecting or forming section that large quantities of gases and water have contact with the binder which contains the pollutant elements, and are contaminated according to a pollution process which is common to all known processes for the manufacture of blankets, mats, or boards of fibers agglomerated by a binder, and which will now be described.
(a) The pollution of the gaseous effluents takes place according to the following process:
The binder is projected into the current made up of fibers and gases, coming from the fiber production apparatus, the binder being present in the form of clouds of fine droplets. Some of this binder is entrapped by the fibers, some is unavoidably deposited on the walls of the installation, and finally some is found in the gases or fumes in the form of fine droplets and in the form of vapor.
Thus two fluid contamination modes coexist, the one consisting of contamination by droplets of the binder and the other consisting of contamination by vapors of the binder. In the binder application, the binder atomization or dispersion devices used furnish particles or droplets within a very wide range of diameters. The finest droplets are not entrapped by the fibers and are drawn through the blanket being formed by the gaseous current, in which they are present in suspension.
The droplets of binder deposited on the fibers during the binder application are subjected to the kinetic effects of the gaseous current passing through the blanket being formed. A large quantity of droplets is extracted from the fibers, migrates through the blanket, and is found in suspension in the exhausted gases.
Finally, the desire to obtain a homogeneous distribution of the binder in the blanket makes it necessary to disperse the binder in the fiber and gaseous current in an area situated near the fiber production apparatus, where this current still has a well-defined geometric form but where its temperature may still be high enough so that some of the binder, or at least its most volatile components, are evaporated. These pollutant vapors mix with the gases and contaminate them.
In the text below, the word "fumes" will be used to designate the gaseous effluents which pass through the fiber blanket and are evacuated outside of the collecting unit, i.e., the gases used for attenuating or guiding the fibers, the fluids induced by these gases, and the pollutant elements in the form of droplets or vapor suspended in these fluids. It is to be understood that various features of the invention, such as treatment steps and components of the apparatus, may be employed with "fumes" having a wide range of compositions and pollutants. It is preferred to treat all components of such fumes, but various features of the invention may also be employed with gases originating in fiber production operations in which the gases have pollutant components, whether or not the pollutants have their origins in fiber binders.
(b) The functions performed by the water in a fiber collecting unit make a large degree of pollution inevitable in any installation in which binders are used.
In operation, water is used:
(1) to dilute and carry the binder when the latter is used in liquid form;
(2) to wash or scrub the fumes, an operation which consists:
(2a) of causing the largest possible amount of pollutants contained in the fumes in the form of droplets or vapor to be captured by the droplets of the scrubbing water, thus causing the pollutant charge of the fumes to be transferred to the wash water;
(2b) of capturing and entraining on the walls of the collecting unit the fibers suspended in the fumes;
(3) to wash the different parts of the collecting installation (perforated belt, fume flues, etc.) in order to evacuate the binder and the fibers deposited therein.
During these operations the wash water is charged with binder components which are soluble, insoluble, or in the vapor state, and the concentration of pollutant elements may reach high values.
The foregoing description of the manner in which the fumes and the water are contaminated is based on an interpretation of measurements and observations made in actual manufacturing installations.
Data derived from such measurement and observation is herein given by way of information; but it will be understood that other data and explanations may be found and that the invention is not limited by the data given.
In all installations for the manufacturing of agglomerated fibrous products, regardless of the fiberization process used, the effluent pollution described above involves considerable quantities of effluents.
In installations equipped with devices for attenuating fibers by blowing, in which the material to be attenuated is transformed into fibers by means of high-energy jets, the quantities of fumes discharged into the atmosphere are--for the best known processes--on the order of magnitude of the following values:
100 Nm.sup.3 per kilo of fibers for the process described in the Slayter U.S. Pat. No. 2,133,236;
300 Nm.sup.3 per kilo of fibers for the AEROCOR process (Stalego U.S. Pat. No. 3,489,243);
70 Nm.sup.3 per kilo of fibers for the SUPERTEL process (Levecque French Pat. No. 1,124,489 and U.S. Pat. Nos. 3,114,618 and 3,285,723);
which, for large production plants, leads to outputs ranging from 50,000 to 1,000,000 Nm.sup.3 /hr. (In these values, Nm.sup.3 refers to the cubic meter volume at standard atmospheric pressure and room temperature.)
In installations equipped with fiber attenuating devices, in which the material to be attenuated is transformed into fibers under the effect of mechanical forces--centrifugal for example--and where a gaseous current is only used as a medium (generally flowing in an essentially horizontal direction, see FIG. 14, for example) for carrying the fibers produced towards the collecting device--the quantity of fumes given off is a little less, but nevertheless very important: for example, 30 Nm3 per kilo of fibers, for the process described in Powell U.S. Pat. No. 2,577,431, which for a production plant results in outputs on the order of 300,000 to 400,000 Nm.sup.3 /hr.
The quantities of polluted water are pretty much the same for all processes, and on the order of 1,000 m.sup.3 /hr. or more for large industrial installations.
The volume of these quantities of polluted effluent has led legislatures first to limit the concentration of phenol compounds in the effluents discarded in the atmosphere, and later to prohibit discarding of any pollutants, at least in certain countries.
Furthermore, limitations concerning the odors or the opaqueness of discharged effluents have been established in various countries.
In addition, installations for the manufacture of agglomerated fibrous products also tent to pollute in another respect. In addition to toxic or pungent-smelling products, these installations discard substantial quantities of steam, on the order of 20 to 30 metric tons per hour for large plants, which steam escapes from stacks in very opaque plumes.
Noise is another type of nuisance created by installations for the manufacturing of agglomerated fibrous products. In these installations, the noise is essentially emitted by two sound sources--the apparatus for producing the fibers and the fan for extracting the fumes.
Actually, all the equipment for producing fibers mounted in these installations uses jets of gases at high speed either for transforming the material to be drawn or attenuated into fibers or for directing the fibers produced. It is known that the acoustic power level emitted by these jets considerably increases with the speed of the jets. This level may exceed 100 decibels adjacent to the fiber production apparatus, where the operators are required to work. This level is much higher than the level tolerated by industrial regulations in many countries.
Furthermore, the acoustic power developed by the fume extraction fan is transmitted along the flues connecting with the fume exhaust stack. The latter is ordinarily situated outside the buildings, where it functions as an antenna, and radiates this acoustic power into the surrounding environment. The inconvenience resulting for the vicinity has caused authorities in different countries to order the shut-down of certain installations.
The need to reduce or eliminate the pollution produced--and this at costs low enough not to overly influence the cost price of the finished product--is pressing. Numerous investigations have been carried out on this problem, and certain solutions have been developed.
The process according to the invention is characterized by the fact that the fumes (as hreinabove defined) are partially recycled, so as to cause them repeatedly to traverse the blanket or mat being formed. The process according to the invention is also characterized by the fact that the majority of the heat contributed by the gases coming from the fiber production apparatus and the attenuated fibrous material is transferred to the wash water, by the fact that the wash water is cooled, by the fact that the fumes are washed in water after they have traversed the blanket or mat and the fiber collecting device in order to transfer to the water some of the pollutant products contained in these fumes, by the fact that the non-recycled part of the said fumes is purified before evacuation into the atmosphere, by the fact that at least some of the wash water is recycled--a certain quantity of which has been subjected to a treatment for extracting at least a sizable fraction of the pollutant products contained in the wash water--and by the fact that the solid wastes are subjected to a purification treatment before final disposal.
The foregoing process effects cooling of the recirculation gases, which is important in making possible such recirculation. In combination with such cooling of the recirculating gases, it is preferred also to spray water on the current of fibers and gases in the receiving chamber, in order to cool the fiber and gas current. Such water spraying, with resultant cooling of the current, together with the cooling of the recirculating gases provides for reduction of the temperatures of the currentnotwithstanding the substantial absence of induction of ambient air by the attenuating blast.
According to a particularly important characteristic of the invention, the quantity of fumes discarded into the atmosphere is essentially equal to the quantity of gases flowing from the attenuating device.
The invention is particularly concerned with recycling the majority of the fumes in the installation, and with treating and evacuating only a small portion of the fumes--it being possible for the recycled portion to reach at least 95% of the total quantity of fumes ordinarily evacuated into the atmosphere. The quantity of fumes to be purified before discarding may thus be less than 5% of all of the fumes, which even makes it practicable to use costly purification treatment, whose effectiveness is total--as for example burning--without prohibitive energy expenditures.
Another object of the invention is to render insoluble the thermohardenable resins contained in the water. These resins are rendered insoluble, according to the invention, by means of a heat treatment--preferably at a temperature greater than 100.degree. C., and more advantageously ranging between approximately 150.degree. and 240.degree. C., and under pressure.
The application of the above process (for rendering resins insoluble) to at least some of the cooling and washing water is advantageously used to render insoluble the dissolved binder components contained in the water, in order to subsequently be able--by means of known techniques--to extract insoluble materials and thus to maintain the concentrations of the pollutant constituents in the washing and cooling waters at a level compatible with the continuous re-utilization of these waters in the installation. The wash water thus circulates in a closed circuit and any external rejection of pollutants with the wash water is eliminated.
Another object of the invention consists of a heat treatment to which the wash water is subjected--a treatment which consists of vaporizing it and of heating this vapor to a temperature sufficient so that the pollutant constituents are transformed into non-pollutant constituents.
The invention also is concerned with means for sound insulation--adjusted to the particulate configurations shown--to the devices for conveying and guiding the recycled fumes, in order to reduce the noise emitted by these devices, and with a particular arrangement of the apparatus for evacuating the non-recycled fumes into the atmosphere, which reduces the noise emitted by this apparatus in the surrounding environment.
In addition to the general objectives above referred to the present invention also contemplates certain controls for the operating conditions, as pointed out just below.
In techniques of the kind briefly referred to above and described in detail hereinafter, the use of the various means for suppression of pollution, especially the recirculation of the current of the attenuating gas and also the separation of the pollutants from the recirculating gas, as by means of a water spray, may at times tend to introduce undesirable fluctuations in the conditions under which the fibers are formed or atteuated, and the condition under which the fiber blanket is formed. Because of the recirculation of a large part of the gases, it is desirable to more completely enclose the forming section, than has been customary where the suppression of pollution by recirculation of the gases is not contemplated. With the more tightly enclosed forming section and where recirculation of gases is employed for the purpose of suppression of pollution, there may be tendencies for fluctuation of both the pressure and the temperature of the gas in the forming section. The pressure will vary in accordance with the quantity of the gases which are diverted and discharged from the recirculation flow path; and in addition, the temperature will vary in accordance with a number of factors including not only the quantity of gas diversion and discharge from the recirculation flow path, but also the extent of water spraying utilized for separation of pollutants from the recirculation gases, as well as the temperature of the water used for such water spraying. Still further, variation in atmospheric conditions, for example as between summer and winter, may also influence the operating conditions with respect to both pressure and temperature.
Variable factors such those just referred to tend to alter uniformity of fiber and fiber blanket production, particularly in the fiber formation by gas blast attenuation, since uniformity of the fibers depends in part upon uniformity of the conditions of temperature and pressure. In fact, if the temperature of the gaseous current and consequently of the fiber blanket is too high, polymerization of the binder will start prematurely, i.e., in for forming section, instead of awaiting feed of the blanket into the binder curing oven. This condition tends to reduce the mechanical properties of the products, particular their resilience.
On the other hand if the temperature of the gases and consequently that of the blanket is too low, the moisture carried by the blanket increases, and this reduces the efficiency of the curing oven, and can even lead to dimensional irregularities of the manufactured products.
Pressure variations tend to adversely influence the effectiveness of the devices used to reduce the pollution in the gases discharged through the stack. A negative pressure in the formation chamber, that is a pressure below atmospheric pressure will increase the quantity of the air penetrating into the forming section and consequently the quantity of gases to be diverted from the recirculation path and discharged. This results in an increase in the quantity of pollutants ejected into the atmosphere. A positive pressure, on the other hand, leads to leakage or discharge from the formation chamber of gases not yet treated, thereby impairing the intended suppression of pollution.
With the foregoing in mind it is contemplated according to the present invention that controls be provided for maintaining substantial uniformity of the conditions prevailing in the zones of fiber attenuation and fiber blanket formation, particularly uniformity of pressure and temperature of the gases in these zones. In addition, it is further comtemplated to regulate the volume of the gas in circulation.
It is also contemplated according to the present invention that the controls for temperature and pressure be adjustable in order to establish the desired pressure and temperature levels.
Other objects and advantages of the invention, including in particular numerous specific advantages for the recycling of fumes, will be given and explained more completely below.